Decreasing device size and increasing device density has traditionally been a high priority for the manufacturing of integrated circuits. Optical lithography has been a driving force for device scaling. Conventional optical lithography is limited to about 80 nm pitch for single exposure patterning. While double and other multi-patterning processes can realize smaller pitch, these approaches are expensive and more complex.
Directed self-assembly (DSA), a technique that aligns self-assembling polymeric materials on a lithographically defined directing or guide pattern, is a potential option for extending lithography beyond its current pitch and resolution limits. The self-assembling materials, for example, are block copolymers (BCPs) that consist of an “A” homopolymer covalently attached to a “B” homopolymer, which are deposited over a lithographically defined directing pattern on a semiconductor substrate. The lithographically defined directing pattern is a pre-pattern (hereinafter “DSA directing pattern”) that is encoded with spatial chemical (e.g., chemical epitaxy) and/or topographical information such as confinement wells (e.g., graphoepitaxy) and serves to direct the self-assembly process and the pattern formed by the self-assembling materials. Subsequently, by annealing the DSA polymers, the A polymer chains and the B polymer chains undergo phase separation to form an A polymer region and a B polymer region that are registered to the underlying DSA directing pattern to define a nanopattern (hereinafter “DSA pattern”). Then, by removing either the A polymer block or the B polymer block by wet chemical or plasma-etch techniques, a mask is formed for transferring the DSA pattern to the underlying semiconductor substrate.
Often, patterns that are desired or targeted (hereinafter “DSA target patterns”) to be fabricated on a semiconductor substrate via a DSA process are created in a design layout during the design phase of an integrated circuit. Generating a photomask for lithographically defining a DSA directing pattern to form the shape of a DSA pattern that accurately corresponds to the shape of a DSA target pattern requires proper accounting of a multitude of physical effects that occur during the DSA process including from photomask writing on through to etching of the phase separated self-assembly materials to form the DSA pattern. For instance, a typical DSA process involves fabrication of a patterned photomask to be used to make the DSA directing pattern, exposing this photomask in a lithographic tool to photoresist that is disposed on a semiconductor substrate, developing the exposed resist, processing the semiconductor substrate to create the DSA directing pattern, spin coating the pre-patterned semiconductor substrate with BCP, and annealing and developing the BCP to form the DSA pattern, followed by a transfer of the pattern of the developed BCP into the substrate by means of etching. Unfortunately, current approaches for defining DSA directing patterns to form the shapes of DSA patterns that correspond to the shape of DSA target patterns do not fully account for the physical effects that occur during the DSA process and/or the DSA target patterns themselves are not DSA compatible so as to be accurately or fully formed via the DSA process.
Accordingly, it is desirable to provide methods for fabricating integrated circuits including generating a photomask for lithographically defining a DSA directing pattern to form a DSA pattern that accurately corresponds to a DSA target pattern. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.